Control system and control method for cogeneration system

ABSTRACT

A control system for cogeneration system provides operation combination calculating means which calculates the combination of operations capable of keeping the voltage of the distribution line within a predetermined tolerance within voltage tolerance based on following (1)-(3). (1) the predicted value of the electric power demand of each customer calculated by electric power demand predicted value calculating means; (2) the impedance of the distribution line recorded by distribution line information recording means; and (3) the combination of cogeneration systems to be operated, as calculated by operation combination calculating means.

CLAIM OF PRIORITY

The present application claims priority from Japanese application serialno. 2005-283231, filed on Sep. 29, 2005, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a control system and a control methodfor a cogeneration system.

BACKGROUND OF THE INVENTION

In recent years, problems of global warming and depletion of naturalresources have begun surfacing. There has been a growing concern overthe effective use of energy. Particularly in the field of globalwarming, the Kyoto Protocol providing for a CO₂-reduction goal tookeffect. During the period from 2008 through 2012, Japan is required toreduce the CO₂ emission volume by 6% with reference to the 1990 level.Against this background, the distributed power generation providedinside the customer, can be utilized in the form of a cogenerationsystem that allows the customers to use not only the generated electricpower, but also the waste heat having been unused heretofore. From theviewpoint of effective use of energy, it is expected to come intowidespread use.

When the distributed power generation has come into widespread use, itis expected to meet the following requirements:

(1) Operate the distributed power generation at a high efficiencyaccording to the actual load.

(2) Maintain the electric power quality of the distribution system incase there is a reverse flow into the distribution system.

In the “cogeneration network system for household use” described inJapanese Patent Laid-open No. 2003-134674 (Patent Document 1), thedistributed power source installed in each customer in a electric powernetwork formed by a plurality of customers is operated on a selectivesources in response to the electric power demand and heat demand of eachcustomer, and the electric power generated by the distributed powergeneration is interchanged among the customers. This arrangementprovides a system for ensuring an effective supply of electric power andheat to the customers within the electric power network.

Moreover, in the “electric power quality maintenance support method andsystem in the distribution system” described in Japanese PatentLaid-open No. 2004-274812 (Patent Document 2), when the voltage of thedistribution system is not kept within tolerance, the specific customerdistributed power generation and system control device are controlled bythe command value based on the computation result of simulation, wherebythe system voltage can be kept within the tolerance.

SUMMARY OF THE INVENTION

The Patent Document 1 discloses the technique wherein some of thecogeneration systems for household use installed at customers of theelectric power network are operated at high power, and the electricpower that cannot be consumed by some customers is supplied to othercustomers. This ensures an efficient supply of electric power and heatenergy to the customers in the network.

Electric power from a high voltage system is usually supplied to a lowvoltage electric power distribution system through a pole transformer.In this case, the voltage of the electric power distribution system isstipulated to remain within 101±6 volts by the Electricity EnterprisesLaw. In case no distributed power generation is available in eachhousehold, or distributed power source is installed in each householdbut the reverse flow is not tolerance, the voltage of the electric powerdistribution system is gradually reduced from the pole transformer tothe terminal costumer, as shown in FIG. 10. In this case, the voltage ofthe electric power distribution system can be kept within the toleranceby adequately setting the voltage value just at the back of thetransformer, the number of customers under the charge of onetransformer, and the length and size of the distribution line (or thenumber of distribution lines).

However, in the Patent Document 1 wherein there is a reverse flow fromthe distributed power generation to the electric power distributionsystem, the voltage of the electric power distribution system may getout of the range of tolerance, depending on the selection of thecogeneration system, as shown in FIG. 11 (operation of the distributedpower generation system marked by a slant line). This may deterioratethe electric power quality. In FIG. 11, the reference numeral 1101denotes a control apparatus, 1102 a communication network line, 1103 adistribution line, 1104 a customer, 1105 a distributed electric powergeneration system, 1106 a hot water pipe and 1107 a electric power line.

According to the Patent Document 2, if the voltage of the electric powerdistribution system is not kept within the tolerance, the distributedpower generation and system control devices of the customer arecontrolled in response to the command value based on the computationresult of simulation, whereby the voltage of the electric powerdistribution system is kept within the tolerance.

In this case, however, to maintain the electric power quality of theelectric power distribution system and to control the distributed powergeneration or system control devices on a priority basis, devices areoperated without due consideration given to the energy demand of thecustomer, particularly to the heat demand. From the viewpoint of energysupply, this will lead to an increase in energy consumption, withouteffective use of the waste heat, or this will lead to a cost increase.In addition to this problem, the following problem also arises: Aftermaking sure that the measured value of voltage in the electric powerdistribution system is out of the tolerance, the distributed powergeneration and system control devices are controlled in real time, andthe voltage quality is maintained. Accordingly, the on-off operations ofthe distributed power generation and system control devices may beperformed too frequently or a time lag may occur in handling.

According to the aforementioned conventional art, an efficient supply ofthe electric power and heat from the electric power supply of eachhousehold connected to the low-voltage electric power distributionsystem is not compatible with the maintenance of electric power qualityof the electric power distribution system. The conventional art fails tomeet these two requirements simultaneously. In order to meet these tworequirements simultaneously, it is necessary to measure the electricpower of each household required to ensure efficient supply of electricpower and heat from the distributed power generation, and the voltage ofeach household required to maintain the electric power quality of theelectric power distribution system.

The object of the present invention is to provide a control system andcontrol method for a cogeneration system which can ensure an efficientsupply of electric power and heat while maintaining the high electricpower quality of a electric power distribution system.

One of the features of the present invention is found in that thecontrol system for the cogeneration system of the present invention isdesigned to supply customers with electric power and heat, and tocontrol a plurality of cogeneration systems connected to a distributionline, and this control system comprises:

electric power demand predicted value calculating means for calculatingthe predicted value of the electric power demand for each of thecostumers;

distribution line information recording means for recording theimpedance of the distribution line;

operation priority calculating means for calculating the priority ofoperation based on the amount of the hot water stored by a customer orthe demand for hot water used by a customer;

operation combination calculating means for calculating the combinationsof cogeneration systems to be operated according to the operationpriority calculating means; and

operation combination calculating means within voltage tolerance thatcalculates the combination of operations capable of keeping the voltageof the distribution line within a predetermined tolerance, based on thepredicted value of the electric power demand of each customer calculatedby the electric power demand predicted value calculating means, theimpedance of the distribution line recorded by the distribution lineinformation recording means, and the combination of cogeneration systemsto be operated, as calculated by the operation combination calculatingmeans.

Another feature of the present invention is found in the description ofBest Mode for Carrying Out the Invention.

The present invention provides a control system and a control method forcogeneration system which ensures an efficient supply of electric powerand heat while maintaining the high electric power quality of a electricpower distribution system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram representing the firstembodiment of the present invention;

FIG. 2 is a system configuration diagram representing the detailedconfiguration of the distributed power generation system of the presentinvention;

FIG. 3 is a system configuration diagram representing the detailedconfiguration of the control system of the present invention;

FIG. 4 is a system control flow representing the first embodiment of thepresent invention;

FIG. 5 is a conceptual view representing the method of determining theoperation status of the distributed power generation;

FIG. 6 is a system configuration diagram representing the secondembodiment of the present invention;

FIG. 7 is a system control flow representing the second embodiment ofthe present invention;

FIG. 8 is a system control flow representing the third embodiment of thepresent invention;

FIG. 9 is a system control flow representing the fourth embodiment ofthe present invention;

FIG. 10 is a conceptual view (Part 1) representing the voltagedistribution of a low voltage distribution system according to theconventional art;

FIG. 11 is a conceptual view (Part 2) representing the voltagedistribution of a low voltage distribution system according to theconventional art;

FIG. 12 is a conceptual view representing the voltage distribution of alow voltage distribution system according to the present invention; and

FIG. 13 is a diagram showing the method of calculating the voltage inthe embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the embodiments illustrated in drawings, the followingdescribes the cogeneration system for household use according to thepresent invention.

Embodiment 1

FIG. 1 is a system configuration diagram representing the firstembodiment of the present invention. This system includes a plurality ofhouseholds 1 as customers, a distributed power generation system 2installed in each household to generate electric power and heat, adistribution line 3, a control system for controlling the operation ofeach distributed power generation system, a control system 4 forcontrolling the operation of each distributed power generation system, aelectric power sensor 5 for measuring the electric power flowing into orout of each household, and a voltage sensor 6 for measuring thedelivered voltage just at the back of the pole transformer. Thedistributed power generation system and control system are connected bya communication network line 7 to permit exchange of data and controlcommands. Electric power and hot water generated by the distributedpower generation system are supplied to each household through aelectric power line 8 and a hot water tube 9. The remainder of theelectric power generated by the distributed power generation system,apart from the electric power having been consumed by the household, issupplied to the surrounding households through the distribution line 3.

As shown in FIG. 2, the distributed power generation system 2 contains:a electric power generation section 10 for generating electric power; ahot water storage tank 11 for producing hot water by heat exchange withthe waste heat generated simultaneously with electric power, and storingthis hot water; a control section 12 for controlling the operation ofthe distributed power generation system in response to the command froman operation command section (to be described later) of the controlsystem; a display section 13 for displaying the distributed powergeneration operation status and notifying the costumer; an input section14 for inputting the customer information and instructions; and arecording section 15 for storing the data measured by the distributedpower generation system. The waste heat generated by the electric powergeneration section 10 is sent to the hot water storage tank 11 through awaste heat tube 16. In this case, a prime mover such as an engine, or afuel cell is used as the electric power generation section 10.

The distributed power generation system measures the data on operationtime, the amount of electric power, the amount of hot water in thestorage tank and others. This data is transmitted to the monitoringsection (to be described later) of the control apparatus through thecommunication network line 7 whenever necessary. All apparatuses insidethe distributed power generation system are connected with each other bythe distributed power generation system communication line 17.Information such as various forms of measurement data and commands isexchanged as required. The input section 14 inputs information in thecase of an abnormal situation different from the normal life such asabsence of the resident or visit by a guest. Based on this input valueand past data, the control section 12 predicts daily amount of electricpower and hot water to be consumed. For example, according to the basicinformation on a weekday, holiday or season, reference is made to thepast data based on the basic information. If the resident is absent oris visited by a guest on a particular date, correction is made based onthe input information from the display section, and the amount ofelectric power and hot water to be consumed are predicted.

The following method, for example, can be considered to calculate thepredicted value for amount of electric power and hot water to beconsumed. The past data on the amount of electric power and hot waterconsumed in the past, and temperature data are organized by working outthe average according to the season, weekday or holiday. If that datefalls on a weekday in summer, the average data on the amount of electricpower and hot water consumed on a weekday in summer in the past is usedas a basic predicted value. Further, if the temperature on that date ishigher than the average, electric power consumption is estimated toincrease due to more frequent use of an air conditioner. Thus, the basicpredicted value for the electric power consumption is corrected to ahigher value. If that date falls on a weekday in winter, the averagedata on amount of electric power and hot water consumed is used as thebasic predicted value. Further, if the temperature on that date is lowerthan the average level, there will be an increase in the amount of hotwater to be used. Thus, the basic predicted value for the amount of hotwater to be consumed is corrected to a higher level. If a guest iscoming on that date, there will be an increase in the amount of electricpower used for air conditioners and the amount of hot water to beconsumed. This information is inputted into the input section, wherebythe basic predicted values for the amount of electric power and hotwater to be consumed are corrected to higher levels.

As shown in FIG. 3, the control system 4 contains a monitoring section18 for monitoring various measurement data, a system status estimatingsection 19 for estimating the voltage of each household based on thecalculation of the system status, a priority calculating section 20 fordetermining the priority of operating the distributed power generationsystem from the measurement data of all the distributed power generationsystems, an operation command section 21 for issuing commands for theoperation status of each distributed power generation system based onthe information of the system status estimating section and prioritycalculating section, and an overall recording section 22 for storing thedata on the impedance of the distribution line, in addition to the datasent to the monitoring section. The electric power measurement value bythe electric power sensor and voltage measurement value by the voltagesensor, in addition to the measurement data of the aforementioneddistributed power generation system, are sent to the monitoring section18 through the communication network line 7. The apparatuses inside thecontrol system are connected with each other by a control systemcommunication line 23, so that various forms of measurement data andcommands are exchanged as required.

The distribution line 3 is connected with the high voltage systemthrough a pole transformer. This arrangement ensures that the electricpower in the amount equivalent to the difference between the overallelectric power consumption of each household and the overall the amountof electric power produced in the distributed power generation issupplied from the high voltage pressure.

Based on the electric power value measured by the electric power sensor,the voltage value measured by the voltage sensor and the database of theoverall recording section 22, the system status estimating section 19 ofthe control system 4 performs estimation and calculation of thedistribution system status, thereby estimating the combination of theoperation statuses of the distributed power generation systems whereinthe voltage of the distribution system is kept within the tolerance.

The following describes an example of measuring the voltage of thedistribution system with reference to FIG. 13. The voltage of thedistribution system is calculated, for example, by the followingequation (wherein an approximate expression is used on the assumptionthat “V” does not change much from 1 p.u.).

To start with, the following calculation is performed:P(n)=P _(g)(n)−P ₁(n)Q(n)=Q _(g)(n)−Q ₁(n)

Then the following is calculated sequentially from i=n-1 through 1:P(i)=P(i+1)−R(i+1)·P(i+1)+P _(g)(i)−P ₁(i)Q(i)=Q(i+1)−X(i+1)·Q(i+1)+Q _(g)(i)−Q ₁(i)

Based on the results of the aforementioned equations, the following iscalculated sequentially from i=1 through n:V(i)=V(i−1)−R(i)·P(i)+X(i)−Q(i)

Based on the data sent from the monitoring section 18, the prioritycalculating section 20 of the control system 4 determines the priorityof operating each distributed power generation system.

The data used in this case is exemplified by the amount of hot water tobe stored in each distributed power generation system, and the predictedvalues for the amount of electric power and hot water to be consumed bythe customer. For example, the priority of the distributed powergeneration systems can be determined as follows: In the first place,selection is carried out to determine the distributed power generationsystems that meet the requirements that the amount of hot watergenerated by the distributed power generation system does not exceed thepredicted value for the hot water to be consumed by each costumer andthe daily operation time does not exceed a predetermined period of time.These systems are assigned with priority in such a way that higherpriority is given to the system having a smaller amount of hot water inthe hot water storage tank. To put it more specifically, the followingprocedure is taken.

The amount of hot water to be consumed subsequently in each household(e.g. ten hours) is subtracted from the current amount of stored hotwater of each distributed power generation system. Hot water must besupplied earlier into a hot water storage tank wherein the valueobtained from this subtraction is smaller. Thus, the priority in theoperation of the distributed power generation system must be determinedin the ascending order of this value. Further, when there are aplurality of distributed power generation systems without muchdifference in the amount of stored hot water (e.g. ±10%), higherpriority is given to the distributed power generation system of lessoperation time.

The difference from the Patent Document 1 is found in the fact that thesystem voltage may get out of the tolerance, as shown in FIG. 11,according to the method of operating the distributed power generationsystem disclosed in the Patent Document 1, whereas the present inventionkeeps the system voltage within the tolerance.

The operation command section 21 of the control system 4 finallydetermines the operation status of the distributed power generationsystem, based on two factors—the combination of the operation statusesof the distributed power generation system wherein the voltage of thedistribution system calculated by the system status estimating section19 is kept within the tolerance, and the priority of operationcalculated by the priority calculating section 20.

FIG. 4 is a system control flow representing the first embodiment of thepresent invention. The delivery voltage just at the back of the poletransformer is measured by the electric power sensor, and the electricenergy running in and out of each household is measured by the electricpower sensor (S1). In the system status estimating section of thecontrol system, the estimated value for the voltage of the distributionsystem is obtained by estimation and calculation of the distributionsystem status based on the measured value (S3).

In addition to this estimated voltage value, the measured value (S2) foreach distributed power generation system—e.g. predicted values for theamount of stored hot water in the distributed power generation system,the operation time, the amount of storage and the amount of hot waterconsumed by each customer—are normally sent to the monitoring section 18of the control system. Such data is monitored by the monitoring section18 (S4), and at the same time, is stored by the overall recordingsection 22. Here when the monitored data has exceeded the specifiedcondition,—for example, when the estimated voltage value has exceededthe voltage tolerance, when the operation time of the distributed powergeneration system has exceeded the set value, or when the amount ofgenerated hot water of the distributed power generation system hasexceeded the estimated value of the amount of consumed hot water—themonitoring section 18 reviews the operation status of each distributedpower generation system (S5). Further, it also reviews the operationstatus of the distributed power generation system for each of thespecified times set in advance (S5).

The following procedure is taken to review the operation status of eachdistributed power generation system: The delivery voltage just at theback of the pole transformer is measured by the electric power sensor,and the electric energy flowing in and out of each household is measuredby the electric power sensor (S6). Based on the measured value, theoperation command section 21 of the control system determines theoverall the amount of produced electric power of the distributed powergeneration system (the number of the systems to be operated) (S8).

From an idealistic viewpoint, the overall amount of electric powerproduced should be determined by the “rated output of the distributedpower generation system”×“the number of systems to be operated”, wherebythe distributed power generation system is operated at the rated outputwherein the distributed power generation system has a high efficiency.Here, the electric energy purchased from the system electric power isthe value obtained by subtracting the overall amount of electric powerproduced by the distributed power generation system, from the overallelectric power consumption of each household. Based on the number ofsystems to be operated, the system status estimating section 19 of thecontrol system takes the step of estimation and calculation of theelectric power distribution system to find out what kind of combinationsof the distributed power generation systems will be appropriate toensure that the voltage of the electric power distribution system iskept within the tolerance, when operating the aforementioned number ofdistributed power generation systems (S10).

It is also possible to predict the voltage for the specific time set inadvance using the predicted value for the electric power consumption,and to estimate the combination of the distributed power generationsystems wherein the voltage value is kept within the tolerance. Thisarrangement eliminates the need of reviewing the operation status withinthe specified period of time, and removes the possibility of increasingthe frequency of starting and stopping the distributed power generationsystem and causing a delay in handling.

In the meantime, the priority calculating section 20 of the controlsystem determines the priority of the operation of distributed powergeneration systems, based on the measurement data (S7) of eachdistributed power generation system (S9).

In the final phase, the operation command section 21 of the controlsystem determines the operation status of each distributed powergeneration system, based on the priority in the operation of eachdistributed power generation system and the result of estimating andcalculating the electric power distribution system status (S11).

To determine the operation status of each distributed power generationsystem, it is necessary to ensure that the distributed power generationsystems having a higher priority of operation should be operated. Toachieve this, the following method can be considered, for example. Toput it more specifically, consider the case shown in FIG. 5 whereinthree distributed power generation systems out of six are operated. FIG.5 shows the priority in the operation of the distributed powergeneration systems and the combination of the distributed powergeneration systems wherein the voltage value is kept within thetolerance. In the first place, combinations (A) and (B) remain aspossible candidates, according to whether or not the distributed powergeneration system assigned with the top operation priority is operated.Then the combination (A) is selected according to whether or not thedistributed power generation system assigned with the second operationpriority is operated. In this case, this is the final decision. If thefinal decision cannot be reached, this procedure is repeated in thelower order of priority.

In the aforementioned example, the electric power generated by thedistributed power generation system during the operation is supplied toeach household through a distribution line. As a result, the distributedpower generation system is operated at the rated output wherein thehighly efficient operation is performed. This arrangement ensures ahighly efficient energy supply as a total system, as compared to thecases where the distributed power generation system is separatelyoperated in each household only for the required electric power.

The following describes the effects of the present invention. Theaverage amount of electric power produced for each household isgenerally 0.3 through 0.5 kW. Thus, when the distributed powergeneration system having a electric power capacity of 1 kW isindependently operated in each household, operation is performed at anapproximate output of about 0.3 through 0.5 kW (30 through 50% of therated output). This reduces the operation efficiency. In the meantime,for example, when a distributed power generation system is used in tenhouseholds, the total electric power consumption is approximately 3through 5 kW. Three through five distributed power generation systemsare selected for operation, the distributed power generation systems canbe operated at the rated output at all times.

At the same time, the voltage of the low voltage distribution system,for example, can be kept within the tolerance, as shown in FIG. 11.Thus, the voltage in the form illustrated in FIG. 12 can be kept withinthe tolerance. In this case, only the electric energy flowing into andout of each customer should be measured. This eliminates the need ofmeasuring the voltage for the purpose of maintaining the electric powerquality of the distribution system.

When there are a great number of the customers under the charge of onepole transformer or the distribution line is longer or thinner (or thereare a smaller number of distribution lines), the voltage fluctuation ofthe distribution system is easily affected by the electric power demandof the customer or the amount of electric power produced by eachdistributed power generation system. This requires the normal systems tobe reinforced. Since electric power quality can be maintained even inthis case, the equipment investment cost for the distribution system canbe placed under control. Further, even there is some change in thedelivery voltage just at the back of the pole transformer, the electricpower quality of the distribution system can be maintained. This featureeliminates the need of an electric utility making efforts to ensure thatthe delivery voltage just at the back of the pole transformer is keptunder strict control. This allows the electric utility to cut down themanagement cost and equipment investment.

Comparison will be made between the Patent Document 2 and the presentembodiment. In Patent Document 2, the operating conditions of thedistributed power generation systems are determined only from theviewpoint of maintaining the electric power quality. No consideration isgiven to the possibility of using the waste heat from the distributedpower generation. In the Patent Document 2, the distributed powergeneration systems are operated independently of the calorific value tobe consumed. This leads to a greater possibility of resulting inexcessive or insufficient amount of waste heat from the distributedpower generation systems. To be more specific, the waste heat from thedistributed power generation system in the Patent Document 2 is lesseffectively used than that in the present invention.

Embodiment 2

FIG. 6 is a system configuration diagram representing the secondembodiment of the present invention. In the example in FIG. 6, theinstallation positions of the electric power sensor and voltage sensorare different from those in the first embodiment (FIG. 1). In thisexample, a electric power sensor for measuring the electric energy justat the back of the pole transformer and a voltage sensor for measuringthe voltage at the measurement point installed in each household areprovided.

FIG. 7 is a system control flow representing the second embodiment ofthe present invention. In the second embodiment, the voltage of thedistribution system is measured by the voltage sensor installed in eachhousehold (S1). Accordingly, the measured voltage value measured by thisvoltage sensor is transferred to the monitoring section of the controlsystem through the communication network, and is monitored by themonitoring section in real time (S3).

The system status estimating section 19 of the control system estimatesthe electric energy at each household, based on the electric energy justat the back of the pole transformer measured by the electric powersensor and the voltage measured by the voltage sensor installed at eachhousehold (S5).

Then the total electric energy consumed by each household is calculatedto determine the number of the distributed power generation systems tobe operated (S7). To put it more specifically, the total electric energyand the number of the distributed power generation systems to beoperated are determined by the following steps: Assume, for example,that each of the ten households is equipped with a distributed powergeneration system having a electric power capacity of 1 kW, and thetotal electric energy consumed by ten households is 4.5 kW. In thiscase, four distributed power generation systems should be operated. Thenthe amount of electric power produced by the distributed powergeneration systems is 4 kW, and the remaining 0.5 kW is supplied fromthe system electric power.

The number of the distributed power generation systems to be operateddepends on the heat value consumed in each household. When only a smallamount of heat is consumed, it would be possible to make arrangementsthat the amount of electric power produced by the distributed powergeneration system should be reduced to 3 kW, and 1.5 kW should besupplied from the system electric power.

After that, similarly to the case of the first embodiment, when theaforementioned number of distributed power generation systems are to beoperated, estimation is made to determine the type of a combination ofthe distributed power generation systems that will ensure that thevoltage of the electric power distribution system can be kept within thetolerance (S9).

The priority calculating section 20 determines the operation priority ofeach distributed power generation system, according to the measurementdata (S6) of each distributed power generation system (S8).

In the final step, the operation command section 21 of the controlsystem determines the operation status of each distributed powergeneration system according to the operation priority of eachdistributed power generation system and the result of the distributionsystem status estimation and calculation (S10).

In the present embodiment, the accuracy of the distribution systemstatus estimation and calculation can be improved by comparison betweenthe measured voltage of the distribution system and the estimatedvoltage and by correction of such data as inductance of the distributionline stored in the overall recording section 22, although this is notillustrated in the control flow of FIG. 7.

In the second embodiment, the same advantages as those in the firstembodiment can be provided. Since only the voltage needs to be measuredby each customer, it is not necessary to measure the electric energyintended to ensure an effective supply of electric power and heat fromthe distributed power generation system.

Embodiment 3

FIG. 8 is a system control flow representing the third embodiment of thepresent invention. The system schematic diagram in this case is the sameas that of FIG. 1.

The procedures up to the steps S7 and S8 in the third embodiment are thesame as those in the first embodiment. After that, based on theoperation priority of the distributed power generation systemsdetermined by the priority calculation section of the control system,the system status estimating section of the control system performs thestep of estimation according to the order wherein the operation priorityof the distributed power generation system is higher, to see whether ornot the distribution system voltage is kept within the tolerance. Thisprocedure is repeated until the distribution system voltage is keptwithin the tolerance. Then it detects the combination of the distributedpower generation systems wherein the distribution system voltage is keptwithin the tolerance, and determines the operation status of eachdistributed power generation system in the final phase (S11).

In the third embodiment, the same advantages as those in the otherembodiments can be provided. Unlike the case of the first embodiment, inthe distribution system estimation and calculation of the controlsystem, it is not necessary to calculate in advance all the combinationswherein the voltage of the distribution system is kept within thetolerance. This arrangement saves the calculation time.

In the third embodiment, the steps S10 and S11 in the control flow ofFIG. 8 are combined after steps S7 and S8 also in the case of the systemconfiguration of FIG. 6 for measuring the electric energy just at theback of the pole transformer and the voltage at the measuring point ofeach household.

Embodiment 4

FIG. 9 is a system control flow representing the fourth embodiment ofthe present invention. The system configuration diagram in this case isthe same as that of FIG. 6.

The procedures up to step S5 in the fourth embodiment are the same asthose of the second embodiment. After that, based on the-operationpriority (S6) of each distributed power generation system determined inthe priority calculating section 20 of the control system, the operationcommand section 21 of the control system temporarily determines theoperation status of each distributed power generation system, andoperates the distributed power generation system (S7). As a result, ifthe value measured by the voltage sensor is kept within the tolerance(S8), the operation continues. If the value measured by the voltagesensor is not kept within the tolerance (S8), a combination of thesecond highest priority is selected according to the result of operationpriority of each distributed power generation system. Then the operationstatus is determined temporarily and the distributed power generationsystem is operated (S7). This procedure is repeated until a decisionstep is taken to determine the operation status of the distributed powergeneration system wherein the voltage of the low-voltage distributionsystem is kept within the tolerance.

In the fourth embodiment, the same advantages as those in the otherembodiments can be provided. Unlike the case of the second embodiment,there is no need of estimating and calculating the distribution systemstatus. This eliminates the need of providing a system status estimatingsection of the control system.

The aforementioned embodiments of the present invention takes intoaccount the demand for electric power and heat by the customers withinthe low-voltage distribution system, thereby ensuring both an effectivesupply of electric power and heat to each customer and maintenance ofthe electric power quality of the distribution system.

When there are a great number of the customers under the charge of onepole transformer or the distribution line is longer or thinner (or thereare a smaller number of distribution lines), the voltage fluctuation ofthe distribution system is easily affected by the electric power demandof the customer or the amount of electric power produced by eachdistributed power generation system. This requires the normal systems tobe reinforced. Since electric power quality can be maintained even inthis case, the equipment investment cost for the distribution system canbe placed under control. Further, even there is some change in thedelivery voltage just at the back of the pole transformer, the electricpower quality of the distribution system can be maintained. This featureeliminates the need of an electric utility making efforts to ensure thatthe delivery voltage just at the back of the pole transformer is keptunder strict control. This allows the electric utility to cut down themanagement cost and equipment investment.

1. A control system for cogeneration system for supplying customers withelectric power and heat, and controlling a plurality of cogenerationsystems connected to a distribution line, said control systemcomprising: electric power demand predicted value calculating means forcalculating the predicted value of the electric power demand for each ofsaid costumers; distribution line information recording means forrecording the impedance of said distribution line; operation prioritycalculating means for calculating the priority of operation based on theamount of the hot water stored by a customer or the demand for hotwater; operation combination calculating means for calculating thecombinations of cogeneration systems to be operated according to saidoperation priority calculating means; and operation combinationcalculating means within voltage tolerance that calculates thecombination of operations capable of keeping the voltage of thedistribution line within a predetermined tolerance, based on thepredicted value of the electric power demand of each customer calculatedby said electric power demand predicted value calculating means, theimpedance of the distribution line recorded by said distribution lineinformation recording means, and the combination of cogeneration systemsto be operated, as calculated by said operation combination calculatingmeans.
 2. The control system for cogeneration system described in claim1, wherein said operation priority calculating means assigns a highpriority to the cogeneration system wherein the amount of stored hotwater is smaller or the demand for hot water is higher.
 3. The controlsystem for cogeneration system described in claim 1, wherein saidoperation combination calculating means within voltage tolerancecomprises the steps of: calculating the distribution line voltage whenthe operation is performed by the combination of the cogenerationsystems to be operated, as calculated by said operation combinationcalculating means, wherein said step of calculating the distributionline voltage is based on the impedance of the distribution line recordedby said distribution line information recording means; and calculating acombination of operations wherein the calculated voltage is kept withina predetermined tolerance.
 4. The control system for cogeneration systemdescribed in claim 1, wherein said electric power demand predicted valuecalculating means calculates the predicted value for electric powerdemand of each customer, based on the meteorological information duringthe period under control and statistic information on the past electricpower demand.
 5. A control system for cogeneration system for supplyingcustomers with electric power and heat, and controlling a plurality ofcogeneration systems connected to a distribution line, said controlsystem comprising: electric power demand predicted value calculatingmeans for calculating the predicted value of the electric power demandfor each of said costumers; distribution line information recordingmeans for recording the impedance of said distribution line; operationpriority calculating means for calculating the priority of operationbased on the amount of the hot water stored by a customer or the demandfor hot water; operation combination calculating means for calculatingthe combinations of cogeneration systems to be operated according tosaid operation priority calculating means; operation combinationcalculating means within voltage tolerance that calculates thecombination of operations capable of keeping the voltage of thedistribution line within a predetermined tolerance, based on thepredicted value of the electric power demand of each customer calculatedby said electric power demand predicted value calculating means, theimpedance of the distribution line recorded by said distribution lineinformation recording means, and the combination of cogeneration systemsto be operated, as calculated by said operation combination calculatingmeans; and control means for controlling the amount of electric powerproduced by each cogeneration system, based on the combination ofoperations wherein the voltage of the distribution line calculated bysaid operation combination calculating means within voltage tolerance iskept within a predetermined tolerance.
 6. The control system forcogeneration system described in claim 5, wherein said operationpriority calculating means assigns a high priority to the cogenerationsystem in which the amount of stored hot water is smaller or the demandfor hot water is higher.
 7. The control system for cogeneration systemdescribed in claim 5, wherein said operation combination calculatingmeans within voltage tolerance comprises the steps of: calculating thedistribution line voltage when the operation is performed by thecombination of the cogeneration systems to be operated, as calculated bysaid operation combination calculating means, wherein said step ofcalculating the distribution line voltage is based on the impedance ofthe distribution line recorded by said distribution line informationrecording means; and calculating a combination of operations wherein thecalculated voltage is kept within a predetermined tolerance.
 8. Thecontrol system for cogeneration system described in claim 5, whereinsaid electric power demand predicted value calculating means calculatesthe predicted value for electric power demand of each customer, based onthe meteorological information during the period under control andstatistic information on the past electric power demand.
 9. A controlmethod for cogeneration system for supplying customers with electricpower and heat, and controlling a plurality of cogeneration systemsconnected to a distribution line, said cogeneration system controlsystem comprising: electric power demand predicted value calculatingprocedure for calculating the predicted value of the electric powerdemand for each of said costumers by means of computing means;distribution line information recording means for recording theimpedance of said distribution line; operation priority calculatingprocedure for calculating the priority of operation by means ofcomputing means, based on the amount of the hot water stored by acustomer or the demand for hot water; operation combination calculatingprocedure for calculating the combinations of cogeneration systems to beoperated, by means of computing means according to said operationpriority calculating means; operation combination calculating procedurewithin voltage tolerance that calculates the combination of operationscapable of keeping the voltage of the distribution line within apredetermined tolerance, based on the predicted value of the electricpower demand of each customer calculated by said electric power demandpredicted value calculating means, the impedance of the distributionline recorded by said distribution line information recording means, andthe combination of cogeneration systems to be operated, as calculated bysaid operation combination calculating means; and control means forcontrolling the amount of electric power produced by each cogenerationsystem, based on the combination of operations wherein the voltage ofthe distribution line calculated by said operation combinationcalculating means within voltage tolerance is kept within apredetermined tolerance.
 10. The control method for cogeneration systemdescribed in claim 9, wherein said operation priority calculating meansassigns a high priority to the cogeneration system wherein the amount ofstored hot water is smaller or the demand for hot water is higher. 11.The control method for cogeneration system described in claim 9, whereinsaid operation combination calculating procedure within voltagetolerance comprises the steps of: calculating the distribution linevoltage when the operation is performed by the combination of thecogeneration systems to be operated, as calculated by said operationcombination calculating procedure, wherein said step of calculating thedistribution line voltage is based on the impedance of the distributionline recorded by said distribution line information recording procedure;and calculating a combination of operations wherein the calculatedvoltage is kept within a predetermined tolerance.
 12. The control methodfor cogeneration system described in claim 9, wherein said electricpower demand predicted value calculating procedure calculates thepredicted value for electric power demand of each customer, based on themeteorological information during the period under control and statisticinformation on the past electric power demand.